1. Field of the Invention
The present invention relates to a gas sensor element and a gas sensor used for measuring a gas, such as combustion gas or exhaust gas, for example, of a combustor or an internal combustion engine.
2. Description of Related Art
An oxygen sensor or an air-fuel ratio sensor for detecting the concentration of oxygen contained in exhaust gas, or for improving combustion efficiency or controlling the combustion of an internal combustion engine of a motor vehicle, is known.
A technique applied for the oxygen sensor in which a catalyst layer covers a detecting electrode of a gas to be measured is known. This technique is disclosed, for example, in Japanese patent publications JP-A-1-203963, JP-A-2-151755 and JP-A-2002-181769. The catalyst layer includes a porous layer of alumina or titania or the like and noble metal particles supported by the porous layer. Consequently, unburnt gas (H2, NOx, HC, etc.) in the gas to be measured is burnt before the unburnt gas reaches the detecting electrode, which prevents an influence on a measurement, improves a detection accuracy and decreases a deviation of a λ point (λ: air excess ratio).
This catalyst layer is formed by a following method: first, alumina or titania is injected or applied to a solid electrolyte member on which the detecting electrode is formed to form the porous layer; and next, this porous layer is dipped in noble metal salt solution including the noble metal particles or ions, and then dried and sintered to form the catalyst layer in which the noble metal particles are supported by the porous layer. In the catalyst layer thus formed, the noble metal particles are uniformly dispersed and supported by the porous layer.